Spray guns are widely used to apply a liquid to a substrate in a variety of industries. In the known spray guns, the liquid is contained in a reservoir attached to the spray gun from where it is fed to a spray nozzle. On emerging from the spray nozzle, the liquid is atomised and forms a spray with compressed air supplied to the nozzle. The liquid may be gravity fed or suction fed or, more recently, pressure fed by an air bleed from the compressed air line to the reservoir or even from the spray gun itself.
A common application of spray guns is in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. A typical paint finish may require application of a primer, base coat, top coat and a clear lacquer. The presence of contaminants such as solid particles in the liquid to be sprayed can spoil the paint finish and extensive re-working is required to achieve an acceptable paint finish. In some instances, the solid particles may cause blockage of the spray gun itself requiring stripping down and cleaning of the spray gun to remove the blockage. In addition, the blockage may have an adverse effect on the spray and render the resulting paint finish unacceptable so that extensive re-working is again required to produce an acceptable paint finish. Re-working of the paint finish and, where required, unblocking of the spray gun, adds to costs both in terms of materials and time.
It is already known to provide a filter in the reservoir to remove contaminants as the liquid is withdrawn from the reservoir during operation of the spray gun. Typically, the reservoir has an outlet connected to an inlet on the spray gun and the filter is positioned across or within the outlet. The outlet is usually of comparatively small size compatible with the connection to the spray gun. The presence of solid particles in the liquid added to the reservoir can result in blockage of the filter so that flow of the liquid to the spray gun is restricted or, in extreme cases, prevented altogether.
A reduction in the flow of the liquid to the spray gun may have an adverse effect on the spray and the resulting paint finish may be unacceptable so that re-working is again required to obtain an acceptable paint finish. Moreover, opening of the reservoir is required to remove and replace the blocked filter with a new filter. This is time consuming and may require decanting of liquid remaining in the reservoir which is then returned to the reservoir when the new filter is in place. As a result, there is increased risk of spillage and possible introduction of contaminants into the liquid. Furthermore, some liquids require activation prior to spraying and have a relatively short life after activation. Delays caused by blockage of the filter may result in such liquids being unusable thereby adding further to costs.
It is also known to filter the liquid to remove solid particles prior to or when adding the liquid to the reservoir by employing a filter externally of the reservoir. This avoids the need to provide a filter within the reservoir but is usually time consuming due to the capacity of the filter being less than the rate at which the liquid can be freely poured into the reservoir. In addition, there is an increased risk of spillage if the addition of the liquid exceeds the capacity of the filter causing the liquid to overflow. Also, dust or other airborne contaminants may be entrained in the filtered liquid with the resulting potential problems outlined above.
WO 98/32539 discloses a reservoir for a spray gun comprising an outer container and an inner liner that is a close fit in the outer container. The liner is removable allowing a new, clean liner to be inserted when changing the liquid to be sprayed which reduces the amount of cleaning required. In one arrangement FIG. 12), the reservoir has an outlet connectable to the gun at one end and a lid at the other end that can be removed to add paint to the reservoir while attached to the gun. In this arrangement, and all the liquid dispensed by the gun passes through a mesh filter provided inside the liner, and the filter has a size and shape similar to the liner so there is no need for the liquid to be filtered when it is being poured into the reservoir.
WO 02/085533 discloses a reservoir for a spray gun having an inlet opening with a removable closure cap that is accessible when the reservoir is attached to the spray gun to allow liquid to be added to the reservoir without detaching the reservoir from the spray gun. In one arrangement, a removable “drop-in” sock filter can be used in conjunction with the inlet opening to filter liquid added to the reservoir. In this arrangement, the filter is not intended to remain in situ within the reservoir,